End functionalized polymers, such as end functionalized polyisobutylenes, are useful as modifiers in oleaginous compositions, as well as being important starting materials for preparation of useful materials such as polyurethanes and amphiphilic networks. Typically functionalized polymers, such as functionalized polyisobutylenes, are prepared by multistep processes that require isolation of the polymer in at least two steps. However, multistep processes are commercially undesirable.
With the advent of carbocationic living polymerizations, there have been attempts to functionalize the living polymers. The extent of success of these attempts are directly linked to the type of monomer being polymerized. Simple one-pot (or in-situ) chain end functionalization of more reactive carbocationic monomers, like isobutyl vinyl ether, can occur using ionic nucleophilic additives, i.e. methanol, alkyl lithium, etc. (see M. Sawamoto, et al. Macromolecules, 20, 1 (1987).) An additional method for end-capping living polymers with these more reactive cationic monomers is disclosed for coupling of poly(isobutyl vinyl ether) chains with silyl ketene acetals or silyl enol ethers in H. Fukui, et al in Macromolecules, 26, 7315 (1993) and Macromolecules 27, 1297, (1994). However, chain end functionalization does not occur when these additives are added to the living polymerization of less reactive monomers such as isobutylene. (see Z. Fodor, et al, Polym. Prepr. Amer. Chem. Soc., 35(2), 492 (1994).) Addition of the nucleophilic reagents at the end of isobutylene polymerization resulted in the consumption of the catalyst and the formation of t-alkyl chloride chain ends on the polyisobutylene rather than the desired nucleophilic substitution. Consequently, a multi-step process would be required to functionalize a living polymer from these less reactive monomers. Even when one considers that allylic chain ends can be provided by an in-situ functionalization of living polyisobutylene by adding allyltrimethylsilanes at the end of polymerization, (see EPA 0 264 214 or B. Ivan, et al, J. Polym. Sci., Part A, Polym. Chem., 28, 89 (1990) this functionalization limits the choice of chemistries to introduce functional groups, however. Thus, there is a need in the art to provide single and two or three step processes to provide functionalized living polymers comprising less reactive cationic monomers, such as isobutylene.
Electrophilic displacement reactions have thus far not been considered a viable option with living polymers made using strong Lewis acids since it is thought that the concentration of active chain ends is too small for further reaction. While such displacements have been carried out with non-polymeric halides, such as 1-adamantyl, there is no indication that such displacements will be successful with living polymers, such as polyisobutylene.
Recently, functionalization of living polystyrene has been carried out with silyl ketene acetals and silyl enol ethers as disclosed in K. Miyashita, et al, in J. Polym. Sci., Polym. Chem., 32, 2531 (1994). As this system uses a SnCl.sub.4 /R.sub.4 N.sup.+ Cl.sup.- catalyst system to achieve living polymerization, it requires a 200 fold excess of the silyl enol ether to complete the end cap in a quantitative manner. As the authors point out, although this method leads to selective and nearly quantitative end-functionalization, the large excess of silyl enol ether makes this method a less than practical method to derive end-functionalized polystyrenes. The instant invention demonstrates a method which significantly reduces the amount of silyl enol ether to practical levels and achieves end functionalization by appropriate choice of Lewis acid catalyst system.